Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$61.60	6.568%	$65.6459	$65.65	$65.65	$65.60
Purchase #2	$133.98	7.191%	$143.6145	$143.61	$143.60	$143.60
Purchase #3	$239.25	12.583%	$269.3548	$269.35	$269.35	$269.40
Purchase #4	$86.73	3.363%	$89.6467	$89.65	$89.65	$89.60
Purchase #5	$227.27	10.536%	$251.2152	$251.22	$251.20	$251.20
Purchase #6	$50.74	9.818%	$55.7217	$55.72	$55.70	$55.70
Purchase #7	$109.54	7.525%	$117.7829	$117.78	$117.80	$117.80
7 purchase totals =	$909.11		$992.9817	$992.98	$992.95	$992.90